The present invention relates to an orthopedic implant, more particularly to a femoral component for a knee prosthesis. The femoral component has three inside surfaces opposite the bearing surface of the femoral component with at least a posterior surface of the femoral component having a porous coating for tissue in-growth.
In order to treat arthritic knees with prosthetic knee implants surgeons have performed total knee arthroplasty (TKA) in which a tibial component, a femoral component and a patella component are implanted onto a surgically prepared tibia, femur and patella. With regard to the femoral component, typically at least three resected surfaces are formed on the distal femur. These surfaces are the posterior, distal and anterior surfaces of the femur. Typically these cuts are planar, although in some situations, the posterior surface may be rounded. In addition to the posterior, anterior and distal surfaces of the femur, two additional resections may be performed, namely, an anterior chamfer cut and a posterior chamfer cut. If the latter two resections are made, then there are typically five planar surfaces which engage corresponding inner surfaces on the femoral component.
Fixation of the tibial, femoral and patellar component to the resected bone surfaces typically involves the use of bone cement or natural bone tissue in-growth. Knee replacement prostheses designed to be fixated through bone in-growth typically have a porous layer to facilitate the bone in-growth. Such a layer is shown in U.S. Pat. No. 4,550,448 in which two layers of uniform beads are utilized to induce the tissue in-growth. These beads may be coated with an osteoinductive and/or osteoconductive coating. An osteoinductive coating may be a bone morphogenic protein such as OP-1 sold by Stryker Corporation. Osteoconductive coatings might be a calcium phosphate coating, either plasma sprayed or applied by the process of U.S. Pat. No. 5,164,187. Both osteoinductive and osteoinductive materials can be used in combination and can include other therapeutic agents, such as antibiotics, analgesics and other water-soluble agents. Alternately, bone cement may be utilized to fix the prosthesis on the resected distal femur. Such a cement is SIMPLEX® P bone cement sold by Stryker Corporation. Often textured surfaces are formed on the implant in areas which contact bone cement. Such textured surfaces may be in a waffle pattern or patterns with undercuts which allow the bone cement to interdigitate with the implant.